JPS5935281A - Optical reader - Google Patents

Abstract

PURPOSE:To perform fast optical reading operation with high resolution and excellent linearity by converting and input selection signal into a multithreshold logical signal as a complementary output and performing current switching, supplying its output to a photoelectric converting element, and outputting a light proportional signal successively. CONSTITUTION:A multithreshold signal generating circuit 40 converts the external input selection signal into a multithreshold complementary signal, which is inputted to a current switching circuit 41. Then, only a specified TR in a photodiode or phototransistor (TR) array 42 is placed in a charged state. Consequently, the light proportional signalintegrated by time is obtained at both terminals of a load resistance 43.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application With the advancement of information processing equipment such as computers, the importance of sensors as input devices is increasing. The present invention relates to an optical reading device that makes full use of IC circuit technology to optically read information at high speed and with high precision.

Conventional Structures and Problems Conventional optical reading devices include silicon vidicon, MOS target vidicon, etc. In these devices, the access function for sequential reading is performed by deflecting an electron beam. Therefore, it has the advantage of being easy to perform with high resolution, but since it is not completely solid-state, it has disadvantages in miniaturization, low power consumption, etc.

On the other hand, all-solid-state optical reading devices include photodiode arrays or matrices, phototransistor arrays or matrices, photoconductor arrays or matrices, CCD arrays or matrices, and the like. Sequentially reading the information requires the ability to access the sensors in each array or matrix. If the sensor group and the scanning function section are mounted as separate components, the mutual wiring becomes complicated, especially in high-resolution devices. Therefore, as an optical reader in which a sensor group and a skimming section are integrated and formed on a silicon chip,
Type 8 solid state optical readers, CCID (Charge Coupled Image Device) and BBID (Packet Brigade Image Device). These consist of an optical sensor section and a scanning section based on MO5 integrated circuit technology, and although they have high resolution,
There are disadvantages in that the reading speed is slow and contrast cannot be obtained greatly.

OBJECTS OF THE INVENTION The present invention allows a sensor section and a scanning section to be formed on the same chip, and the above-mentioned MO3 type element, CCI
The purpose of this invention is to provide an optical reader with high speed, high resolution, and good linearity, which eliminates the drawbacks of D, BBID, etc., and is mainly based on bipolar integrated circuit technology. When a large number of photodiodes or phototransistors are arranged in an array, such as in an image sensor, and the reading time of a particular element is sufficiently small compared to the total scanning time, operating in charge accumulation mode can significantly improve overall sensitivity. It is well known that it can be done.

In the charge storage mode, charges are stored in the reverse junction capacitance in the case of the photodiode and in the base-collector reverse junction capacitance in the case of the phototransistor b. The timing of operation is the period during which the photocurrent is integrated with respect to time (
The junction capacitance is charged during access, the photocurrent discharges the charged charge during non-access, and the peak of the amount of charge or charging current occurs during the next access. By sensing the value, a light proportional signal is obtained, and the longer the integration time, the greater the sensitivity.The reading speed is determined by the maximum possible frequency of the clock pulse for access.The present invention uses charge accumulation mode. This invention relates to a drive circuit that enables high-speed access to a photodiode or phototransistor that operates at Since all the logic circuits for this operate in a non-saturated manner, it is possible to read without error even if the access clock pulse frequency is 10 MHz or more.

Structure of the Invention In order to achieve the above object, an optical reading device of the present invention includes a multi-threshold signal generation circuit that converts an external input selection signal into a multi-threshold logic signal with complementary outputs, and a constant current source. and a current switching circuit that is cascade-connected and receives the multi-threshold logic signal to access a predetermined one of the plurality of photodetection elements, and receives the light proportional signal of the accessed photoelectric conversion element. The configuration is such that the data are sequentially read out.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, which is a circuit for converting a signal into a multi-threshold logic with complementary outputs (2). The current from the constant current circuit (3) flows through the transistor pairs (4), (5), (6) that constitute the current switching circuit.
The input selection signal (
According to the results of the comparison with 1), the transistor (4a) or (4b) side, the (5a) or (5b) side, the transistor (6a)
or (6b) side, depending on the respective current,
Complementary 8-bit voltages are generated by resistor pairs (7), (8), and (9). The diode string (10,) is Φ
This is to obtain an appropriate voltage level shift from the side chamber source αη, which determines the bias voltage for driving the cascaded current circuit connected to the complementary hydraulic power. Note that this voltage level shift force terminal (la
), complementary output (2) when a “H” level signal is input to
A is "H" and X is "L". This logic amplitude is determined by the value of the resistor pair (7) and the current value of the constant current circuit (3). ), (6)
Since it operates in a non-saturated state, it is extremely fast.

Although FIG. 1 shows the case of 8 bits, this can be expanded to a case with a larger number of bits by repeating the same procedure.

FIG. 2 shows that the multi-threshold logic signal is received at the input terminal (b) and a constant current source is applied to the desired photodiodes (28a) to (28h) (phototransistor).
This photodiode (28a) to (28h)
This circuit is made up of cascaded current switching circuits. Transistor pair (b), (
(to), (to), . . . are resistors (22a) to (22
h) is a load resistor that detects which transistor is in a energized state among the transistor pair αη.

Transistor pair a''h, PNP) transistor (21a
) (21b), load resistors (22a) (22b), and phototransistors (28a) (28b). Of the transistors in the transistor pair a'tt, the PNP transistor (21a) side If the transistor is energized, the collector voltage of the transistor decreases, the PNP transistor (21a) turns on, and a charging current proportional to the intensity of the irradiation light flows through the phototransistor (28a), resulting in a reading period [ The access period is one. This provides an output at Vout that is proportional to the charging current. The collector potential of the transistor on the PNP transistor (21b) side that is not in a energized state among the transistor pair αη becomes a voltage near Vcc (Φ side power supply voltage), and the PNP transistor (21b) connected thereto turns off. , the photodiode (28b) is in a floating state, and the integration period (
(non-access period). Transistor pair) ~ (e)
The same applies to the case of . Further, if the logic amplitude of the input terminal (a) is 0.6 volts, it is sufficient to drive the current switching circuit.

Therefore, according to the present circuit, high-speed reading is possible because the access time delay due to parasitic capacitance can be minimized and the transistor operates in a non-saturated state.

FIG. 8 shows another embodiment of the cascade type current switching circuit, in which the current switching circuit is composed of a pair of PNP transistors, and the photodiode is directly driven by the collector current of the current switching circuit. A pair of transistors @@, C4, OD which receives a multi-threshold signal from a constant current source (E) at its input terminal (F) and operates as a current switching circuit connected in a cascade configuration.

), (to), (goods), some selected branch (
(collector of the transistor). Transistor pair (
A diode array) and a photodiode (to) are attached to the collectors of each of the transistors (b), ni), ni), and (b), respectively, and the cathode side electrodes of the photodiodes (to) are connected in common to vout. and ground terminal (2)
Connect a common load resistor between. The read output is Vo
Obtained from ut. A photodiode with current flowing through it is in a reading state, and a photodiode with no current flowing through it is in an integrating state. By sequentially scanning the branch paths through which current flows, -dimensional information can be sequentially read.

In each of the above embodiments, the case where 23-8 photodiode arrays are accessed has been explained. However, when accessing 2n photodiodes, the multi-threshold logic circuit shown in FIG. 1 can be changed to an n-bit type. Extend and 2nd
This can be realized by expanding the cascade type current switching circuit shown in FIG. 8 or 8 to n stages. Note that, since the circuit of the present invention operates by dividing the current source, it has the characteristic that power consumption can be reduced despite the use of bipolar transistors and transistors.

FIG. 4 is a block diagram of an optical reader according to the present invention. This device is used as a multi-threshold signal generation circuit)
converts the input selection signal into a multi-threshold complementary signal, inputs this signal to the current switching circuit θ■, and selects only a specific photodiode or phototransistor in the photodiode or phototransistor array. The device is placed in a charging state, and thereby a time-integrated light proportional signal is extracted from both ends of the load resistor. The above explanation has been made regarding the case where a photodiode/1' dot is used as a photodetector element, but a bipolar phototransistor can also be connected and used in exactly the same way.

Effects of the Invention As is clear from the above description, according to the present invention, it is possible to realize an optical reading device with high speed, high resolution, and good linearity. Furthermore, all functions can be formed on a silicon chip using a normal bipolar process. Therefore, the present invention is extremely useful as an input device for information processing equipment, and has great industrial effects.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention, FIG. 1 is a configuration diagram of a multi-threshold signal generation circuit, FIG. 2 is a configuration diagram of a current switching circuit, and FIG. 8 is a configuration diagram of a current switching circuit. FIG. 4 is a block diagram of the entire optical reading device according to the present invention. (1) −°/selection signal input terminal,

[2]...multi-threshold signal output terminal, (3)...constant current circuit,
(4J (5) (a)... Current switching transistor pair, (7) (8) (9J...-Resistor H1an...
・Level shift diode string, (B)...Input terminal, 4...Constant current circuit, En(G)CII Qη(G)a
e4... Current switching transistor pair, (21a) ~
(21h) -...Switch transistor, (4)...Load resistor, (2Ba) - (221h)...Photodiode, (2)...Multi-threshold signal generation circuit, (B)...Current switching circuit, )...-photodiode or phototransistor array, ■...load resistance, -...output signal terminal agent Yoshihiro Morimoto No. f factor l

Claims (1)

[Scope of Claims] 1. A multi-threshold signal generation circuit that converts an input selection signal from the outside into a multi-threshold logic signal with a complementary output, a constant current source, and a multi-threshold logic signal that is cascade-connected and An optical reader comprising: a current switching circuit for accessing a predetermined one of a plurality of photodetecting elements in response to a hold logic signal; and configured to sequentially read out optical proportional signals of the accessed photoelectric conversion elements. 2. The multithreshold load signal generation circuit consists of a transistor differential pair whose emitters are connected to a constant current source, a collector resistor connected to each transistor of this transistor differential pair, and a voltage applied to the collector resistor. 2. The optical reading device according to claim 1, further comprising a level-shifting diode array for determining the level, and configured to extract a complementary multi-threshold logic signal from the collector of the differential pair of transistors. 8. Determine the multi-threshold signal generation circuit with a transistor differential pair whose emitters are connected to a constant current source, a collector resistor connected to each transistor of this transistor differential pair, and a voltage to be applied to this collector resistor. 2. The optical reading device according to claim 1, further comprising a level shifting resistor configured to output a complementary multithreshold logic signal from a collector of a differential pair of transistors. 4. The current switching circuit is connected to NP in cascade.
N) consists of a differential pair of transistors, a load resistor connected in series with the cascade circuit, and a PNP)-transistor that senses the current on this load resistor;
) The optical reading device according to claim 1, wherein the optical reading device is configured to switch a photodiode or a phototransistor connected to the transistor with opposite polarity between an access state and a non-access state. 5. PNP connected in cascade for current switching circuit
) The optical system according to claim 1, wherein a transistor differential pair is used, and the PNP is connected to the cascade circuit.) A photodiode or a phototransistor connected with a polarity opposite to that of the transistor differential pair is switched between an access state and a non-access state. formula reader.